/*
* trackball.h
* A virtual trackball implementation
* Written by Gavin Bell for Silicon Graphics, November 1988.
*/

typedef float  Quaternion[4];

/*
* Pass the x and y coordinates of the last and current positions of
* the mouse, scaled so they are from (-1.0 ... 1.0).
*
* The resulting rotation is returned as a quaternion rotation in the
* first paramater.
*/
void Trackball(float q[4], float p1x, float p1y, float p2x, float p2y);

/*
* Given two quaternions, add them together to get a third quaternion.
* Adding quaternions to get a compound rotation is analagous to adding
* translations to get a compound translation.  When incrementally
* adding rotations, the first argument here should be the new
* rotation, the second and third the total rotation (which will be
* over-written with the resulting new total rotation).
*/
void AddQuats(float *q1, float *q2, float *dest);


/*
* A useful function, builds a rotation matrix in Matrix based on
* given quaternion.
*/
void BuildRotMatrix(float m[4][4], float const q[4]);

/*
* This function computes a quaternion based on an axis (defined by
* the given vector) and an angle about which to rotate.  The angle is
* expressed in radians.  The result is put into the third argument.
*/
void AxisToQuat(float a[3], float phi, float q[4]);
